"It argues that there would be no use for two sets of fangs that are incomplete, or some intermediary stage, therefore they must always have existed fully formed."
What would a vegetarian, family friendly, pre-fall black mamba need with these teeth? Did it need them to tackle some tough grass?
Why can't creationists see their own logical inconsistencies? The Mamba was either designed to be a killer which falsifies the assertion that all creatures were vegetarian before the fall, or it was peaceful and it evolved after the fall to be the killer it now is, falsifying the assertion the it could not have evolved such an elaborate set of teeth!